Condition sensing apparatus



Dec. 29, 1959 DEZ'EL 2,919,438

CONDITION SENSING APPARATUS Filed Jan. 8, 1958 3 Sheets-Sheet 1 OUTPUT IN V EN TOR. FRED I DEZIEL j /m wq QM ATTORNEY F. T. DEZIEL Dec. 29, 1959 3 Sheets-Sheet 2 Filed Jan. 8, 1958 IIIIIIIIIIIIIII1|Il|l|\|I\ 1l|\| R .0 o: 8 3 M T. D mmxa a m E Y B J m mp Q. 0w #9 Q. F E A- em. mm? 52% v:

AT TURWE Y Dec. 29, 1959 Filed Jan. 8, 1958 F. T. DEZIEL 3 Sheets-Sheet 3 GEIGER TUBE 3m 9 o 302 OUTPUT Jig: 3

INVENTOR.

FRED T. DEZIEL ATTORNEY United States 2,919,43 CONDITION SENSING APPARATUS Fred T. Deziel, Bloomington, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapohs, Minm, a corporation of Delaware Application January 8, 1958, Serial No. 707,791

10 Claims. (Cl. 340-227) This application is a continuation in part of the copending application of Fred T. Deziel, Serial Number 592,767, filed June 21, 1956, now abandoned.

The present invention is concerned with a condition sensing apparatus and more particularly a condition sensing, apparatus using a condition sensor having a pair of electrodes positioned in an ionizable gaseous medium, for example, a Geiger-Muller tube.

A Geiger tube can be constructed to be sensitive only to the electromagnetic radiations of a wave length which is emitted by a given condition, for example a fire or a flame. Therefore the Geiger tube can be positioned so as to be subjected to sources of radiation other than those characteristics of the given condition. For example, a Geiger tube fire detector can be positioned to be subjected to sunlight or artificial illumination and it will not detect such radiation but will detect a fire in the same region.

A Geiger tube has an inherent feature which can be called the background count of the Geiger tube. The Geiger tube is constructed to have two electrodes, an anode and a cathode, positioned in an ionizable gaseous medium. When electromagnetic wave energy strikes the cathode, electrons are liberated. These electrons pass through the gas to the anode. The gas is ionized and apulse of current passes through the Geiger tube. If the Geiger tube were used for a fire or flame detector, it is desirable to have pulses of current pass through the Geiger tube only upon it being subjected to the fire or flame. However, there is this inherent background count and such background count is always present at least in slight degree.

The use of an integrating or time delay circuit in connection with a Geiger tube to eliminate or discriminate against such background count is known. However, such a construction requires that the time constant of the unit be relatively long. In other words, the time of response to the presence or absence of a fire or flame is limited by such construction.

The present invention provides an improved structure utilizing an integrated signal in combination with a non-integrated signal. It has been found that such a construction more eifectively eliminates, or discriminates-against, the background count while allowing a shorter time constant thereby giving faster detection of the presence or absence of a fire or flame.

It is therefore an object of the present invention to provide a condition sensing apparatus having a condition sensor employing a pair of electrodes in an ionizable gaseous medium and providing a first and a second signal path for amplifying the pulses of current from the condition sensor, one of the signal channels having an integrating or delay circuit therein.

It is a further object of the present invention to provide a condition sensing apparatus having a condition sensor of the Geiger-Muller type and providing an electron discharge device having a first and second control electrode with the voltage from the Geiger-Muller tube 2,919,438 Patented Dec. 29, 1959 being applied directly to one of the control electrodes and through an integrating or delay network to the other electrode thereby rendering the electron discharge device conductive only upon a coincidence of signal on the two control electrodes.

It is a further object of the present invention to provide a condition sensing apparatus utilizing a Geiger tube, which apparatus discriminates against the background count of the Geiger tube by providing a sharp cutoff, electron discharge device, for example, a gated beam tube, having a pair of control electrodes with the output voltage of the Geiger tube applied directly to one of the control electrodes and through a time delay network to the other control electrode of the gated beam tube to thereby cause the gated beam tube to be con trolled only when there is a coincidence of signals on the two control electrodes of the gated beam tube.

It is a further object of the present invention to provide a condition sensing apparatus utilizing a Geiger tube, and to discriminate against the background count of the Geiger tube by providing an electron discharge device having a pair of control electrodes with the output voltage of the Geiger tube being applied to each of the control electrodes through individual integrating circuits, wherein the voltage applied to one of the control electrodes is integrated more than or relative to the voltage applied to the other control electrodes.

These and other objects of the present invention will be apparent to those skilled in the art upon reference to the following specification, claims and drawings of which:

Figure 1 is a schematic representation of a first modification of the present invention showing a combustion detector,

Figure 2 is a schematic representation of a second modification of the present invention, also showing a combustion detector, and

Figure 3 is a schematic representation of a further modification of the present invention.

Referring specifically to Figure l, the reference nu, meral 1i designates a condition sensor of the Geiger- Muller tube type having a first electrode 11 and a second electrode 12 separated by an ionizable gaseous medium. This Geiger tube is of the non-self-quench type. The condition sensor 10 is connected by means of conductors 13 and 14 to an electronic amplifying circuit including electron discharge devices 15, 16 and 17.

Electron discharge device 15 is a gas filled device, for example a Thyratron. Discharge device 15 includes an anode 18, a control electrode 19, a further electrode 20, a cathode 21, and a cathode heater 22. The anode 18 of discharge device 15 is connected to the electrode 12 of condition sensor 15). The control electrode 19 of this discharge device is connected to the electrode 11 of the condition sensor 10.

Electron discharge device 15 and its associated components are a quenching circuit for Geiger tube 10. Operating voltage is applied to electronic means including discharge device 15 from a battery 23 and from a transformer 24. Transformer 24 includes a primary winding 25 and a pair of secondary windings 26 and and 27. Secondary winding 26 is employed to supply energy to the cathode heater 22 of discharge device 15 and to cathode heaters of discharge devices 16 and 17.

30 and 31 to the control electrode 19 of discharge device 15. A test switch 232 is provided to short capacitor 29 through resistor 30. The function of this switch will be described.

The operating voltage for discharge device 15 and condition sensor 19 is supplied from battery 23. The negative terminal of battery 23 is connected directly to the cathode 21 and the positive terminal is connected to the anode 18 through a resistor 32 shunted by a capacitor 33.

The voltage across parallel combination of resistor 32 and capacitor 33 is controlled by condition sensor 19. In other words, when the condition sensor 10 is subjected to a condition which causes its gas to ionize, a voltage appears across parallel connected resistor 32 and capacitor 33 due to conduction of discharge device 15. The upper terminal of this resistor capacitor combination is connected directly to cathode 34 of discharge device 16. The lower terminal of this resistor capacitor combination is connected first through resistor 35 to control electrode 36 of discharge device 16, and second through resistor 37 to control electrode 38 of discharge device 16.

Referring now specifically to discharge device 16, this discharge device may be a gated beam type device for example a 6BN6. This device includes an anode 39, control electrodes 36 and 33, a further electrode 4d, and a cathode heater 4d. It is a characteristic of a gated beam tube that the tube is capable of cutting itself ofi due to tube current.

Operating voltage for the electronic stage including discharge device 16 is provided from a pair of batteries 42 and 43. Battery 42 has its negative terminal connected directly to cathode 34 and its positive terminal connected to electrode 49 through a resistor 44 and to anode 39 through a plate load resistor 4-5. to battery 43 is essentially a biasing source of voltage for electron discharge device 16 and has its positive terminal connected directly to cathode 3 and its negative terminal connected through resistors 46 and 47 respectively to the control electrodes 36 and 33. The voltage magnitude of battery 43 is such as to normally bias discharge device 16 to cut-off.

A capacitor 43 is provided and is connected between the control electrode 38 and the cathode 34- of discharge device 16. This capacitor 48 in combination with resistor 37 comprises an integrating or time delay network. Assume for the moment that a voltage is developed across the parallel connected resistor 32 and capacitor 33. This voltage is applied directly between the control electrode 36 and the cathode 3d of discharge device 16. However, the integrating network of resistor 37 and capacitor integrates this current and applies a voltage to the control electrode 33 with respect to the cathode 34 only after a time delay. it is necessary in the electronic circuit including the discharge device 16 that a signal voltage appear on the control electrodes 36 and 33 at the same time in order for the discharge device 16 to conduct. in other words, there must be a coincidence of voltages on these two control electrodes. if the condition sensor 1% has responded to a random condition, or a backgrount count, the voltage present on the control electrode 36 will disappear before a voltage can be applied to the control electrode 38, Therefore, the discharge device 16 does not conduct and the condition sensing apparatus discriminated against the background count which causes the condition sensor 16 to ionize.

Referring now to discharge device 17, this discharge device includes an anode d, a control electrode 51, a cathode 52 and a cathode heater 53. The control electrode 51 and the cathode 52. are connected across the plate load resistor 45 associated with discharge device 16 and therefore discharge device 17 is controlled in accordance with the state of conduction or nonconducticn of discharge device 16. Operating voltage is applied to the discharge device 17 from a battery 54 having its negative terminal connected directly to the cathode 52 and having its positive terminal connected to the winding 55 of a relay 56 to the anode 50. A filter capacitor 57 is provided in parallel with the winding 55.

Relay 56 has been shown to include a movable switch blade 53 and a stationary contact 59 which are conected to a pair of terminals labeled output. It is recognized that relay 56 may have a plurality of switch blades and contacts and that a variety of functions can be accomplished by the action of this relay. However, for purposes of simplicity a single pair of contacts have been shown and the control effect of these contacts has been labeled output.

The apparatus of Figure 1 is a fire detector. In order to construct a fire detector, that is a detector which is to actuate an alarm or perform another control function upon a fire being established in an area, which is fail safe the relay must be energized in the absence of fire. This is the apparatus as shown in Figure 1. This is a fail safe arrangement since if the discharge device 17 for example should fail, relay 56 will drop out and falsely indicate the presence of fire at the location of the condition sensor ltl. While this is a false indication, it performs a control function which makes it evident that a fault has occurred within the fire detector and this fault can be corrected in a short period of time.

The apparatus of Figure 1 is shown in the standby condition. Electrical power is applied to the primary winding 25 of transformer 24, the condition sensor 10 is not subjected to a fire, electron discharge device 15 biased to cutoff by the voltage across capacitor 29, electron discharge device 16 is biased to cutoff by battery 43, and electron discharge device 17 is conducting to maintain relay 56 in the energized condition. If it is desired to test operation of the condition sensing apparatus, test switch 232 can be closed. This causes the cutofl voltage to disappear from the control electrode 19 of discharge device 15 and this discharge device conducts to develop a voltage across the parallel connected resistor 32 and capacitor 33. The polarity of this voltage is such that a negative voltage appears at the upper terminal thereof and a positive voltage appears at the lower terminal thereof. A positive voltage is therefore applied to the control electrodes 36 and 38 of discharge device 16. After a time period during which the test switch 232 must be held closed, the signal appears simultaneously at the control electrodes 36 and 38 of discharge device 16 and this discharge device conducts to develop a voltage across plate load resistor 45. The polarity of this voltage is such as to be negative on the upper terminal thereof and positive on the lower terminal thereof. This voltage is of a magnitude to bias discharge device 17 to cutoff and thereby cause relay 56 to be de-energized. This indicates that the condition sensing apparatus, exclusive of the condition sensor 10, is operating properly.

Considering the condition now where test switch 232 is open and the condition sensor 10 is subjected to a random condition or a background count, a pulse of current passes between electrodes 11 and 12. This current path can be traced from the right hand terminal of battery 23 through resistor 32, conductor 14, condition sensor 10, conductor 13, resistors 31 and 30, diode 28, and secondary winding 27 to the left hand terminal of battery 23. This current flow develops a voltage across resistors 31 and 30 such that a positive voltage is applied to control electrode 19 with respect to cathode 21. This causes discharge device 15 to conduct and develop a voltage across resistor 32 and capacitor 33. This voltage can be considered the output of condition sensor 10 and this voltage produces two effects.

First, substantially all of the voltage from battery 23 now appears across resistor 32 and therefore an operating voltage is no longer available for condition sensor and condition sensor 10 becomes extinguished. This is the extinguishing feature of the electron circuit. Second, this voltage is applied directly to the control electrode 36 of the discharge device 16 and is applied to the control electrode 38 of this discharge device through an integrating or time delay network. Unless a signal appears at those two control electrodes at the same time discharge device 16 will not be rendered conductive.

' The function of capacitor 33 is to provide a certain decay time for the voltage developed across resistor 32 and capacitor 33 in parallel. This decay time determines the firing rate of the Thyratron discharge device 15. In other words, the voltage which has been developed across resistor 32 due to discharge device firing causes capacitor 33 to be charged and until this charge has leaked off, an operating voltage is not available either for the Geiger tube Iii-or for the discharge device 15.- After a time period however, a sutficiently high operating voltage is again applied to condition sensor 10 and discharge device 15 and if the condition sensor 10 is again subjected to a condition which ionizes its gas a further pulse of voltage appears across resistor I 32 and capacitor 33.

In the case of a random or background count, presently being considered, such a further ionizing event does not occur and discharge device 16 remains nonconductive due to the fact that a coincidence of signal voltage does not occur on the control electrodes 36 and 38.

Consider now the case of condition sensor 10 being subjected to a fire so that the ionizable gas is continuously subjected to electromagnetic radiations which cause the gas to ionize. In this case, the condition sensor 111 and the Thyratron 15 will be continuously cycled between a conducting and a non-conducting state and a cycling voltage will be applied to the capacitor 33 and the resistor 32.

After the given time delay as determined by the capacitor 48 and the resistor 47, a voltage appears across capacitor 48 of a sufiicient magnitude to cause discharge device 16 to conduct. Explaining this more fully, the voltage developed across capacitor 33 and resistor 32 is immediately applied through resistor 35 to control electrode 36 and cathode 34. The same voltage is applied through resistor 37 to control electrode 38 and cathode 34. However, capacitor 48 is connected between control electrode 38 and cathode 34. It is a well known electrical characteristic of a capacitor that in an uncharged state and when connected in series with a resistor to a source of voltage, the capacitor voltage builds up at an exponential rate as determined by the capacitance value of the capacitor and the resistance value of the resistor. The capacitor 48 and resistor 37 have been selected so that the voltage does not build up across capacitor 43 to a sufiicient magnitude to cause discharge device 16 to conduct unless the condition sensor 10 is subjected to a sustained condition such as a fire to cause a sustained pulsing of both the condition sensor 10 and the discharge device 15.

Conduction of discharge device 16 causes a voltage to be developed across plate load resistor 45 and this in turn applies a negative voltage to the control electrode 51 of discharge device 17 to cause this discharge device to be biased to cutoff thereby causing relay 56 to drop out. Switch blade 53 therefore disengages contact 59 and a control effect of one type or another is actuated to indicate that a fire exists at the location of the condition sensor 10.

The apparatus of Figure 1 has been constructed using components of the following values. It is intended that such values be exemplary only and they do not constitrue a limitation of the present invention.

Discharge device 15 5696 Discharge device 16 6BN6 Discharge device 17 12AU7 Battery 23 v.D.C 200 Battery 43 v.D.C.. 18 Battery 42 v.D.C.. 225 Battery 54 v.D.C.. 250 Winding 26 v.A.C 6.3 Winding 27 ..v.A.C 6.3 Capacitor 29 mfd 4 Capacitor 33 mfd 0.05 Capacitor 48 mfd 4 Capacitor 57 mfd 4 Resistor 30 ohms 10K Resistor 31 megohms 10 Resistor 32 do.. 1 Resistor 35 do 1 Resistor 37 do 1 Resistor 44 ohrns 68K Resistor 45 do 39K Resistor 46 megohms 1 Resistor 47 do 1 Referring now to Figure 2, the apparatus of Figure 2 is a flame detector, as distinguished from a fire detector. A flame detector is a type of device which is normally associated with a heating system wherein a combustile fuel is burned and the flame detector is provided to sense the presence or absence of flame and thereby control associated components, for example a safety switch or a main fuel valve, and prevent unlimited feed of the combustion fuel to the combustion chamber when the flame has become extinguished.

The apparatus of Figure 2 has been shown as a two unit apparatus. The reference numeral 60 designates a first unit which is essentially an electronic amplifier having an electron discharge device 61, an electron discharge device 62 and a further electron discharge device 63. The reference numeral 64 designates a second unit which can be called a detector unit having an electron discharge device 65 and a condition sensor 66 having a first electrode 67 and a second electrode 68 positioned in an ionizable gaseous medium.

Drawing an analogy between the apparatus of Figure 2. and Figure 1, the condition sensor 66 may be the Geiger-Muller tube 10 of the apparatus of Figure 1. The electron discharge device 65 may be the Thyratron 15 of the apparatus of Figure 1. The electron discharge device 61 may be the gated beam tube 16 of the apparatus of Figure 1.

Describing first the apparatus designated by the reference numeral 60, this apparatus includes signal input terminals 164-, 165, and 166. The apparatus likewise includes power input terminals 167, 168, 169 and 171). The terminals 167 through 170 are connected to an alternating current source of voltage, not shown.

Electron discharge device 61 includes an anode 71, a first control electrode '72, a second control electrode 73, a further electrode 74-, a cathode 75, and a cathode heater 76. Electron discharge device 62 includes an anode 77, a control electrode 78, a cathode 79, and a cathode heater 80. Electron discharge device 63 includes an anode 81, a control electrode 82, a cathode 83 and a cathode heater 84.

Operating voltage for discharge devices 62 and 63 is supplied from a secondary winding 85 of transformer 86 having a primary winding 87 connected to power input terminals 169 and 170 and having secondary windings 88 and $9. The cathode 73 of discharge device 62 is connected to the left hand terminal of secondary $5 and anode 77 is connected through a resistor 90 to a tap 91 of secondary 85. The control electrode 82 and cathode 83 of discharge device 63 are connected to resistor 90 so that the discharge device 62 is effectively placed in controlling relation to the discharge device 63. The discharge device 62 is normally conducting and during the half cycle that the tap 91 is positive, a voltage is developed across resistor 90 of sufiicient magnitude to bias discharge device 63 to cut-oflf. The anode 81 of discharge device 63 is connected through winding 92 of a relay 93 to the right hand terminal of secondary 85 and it can therefore be seen that at the time discharge device 62 is conducting a positive voltage is applied to the anode of discharge device 63. However, due to the voltage developed across resistor 96 discharge device 63 remains nonconductive.

Discharge device 63 is connected to control energization of winding 92 of relay 93. Relay 93 includes a movable switch blade 94 and a stationary contact 95. The switch blade and stationary contact have been shown connected to terminals labeled output. It is to be recognized that relay '93 may have a variety of switch blades and contacts which perform a number of control functions dependent upon condition of energization of winding 92.

Secondary winding 88 of transformer 86 is provided to supply voltage to the cathode heaters 76, 80 and $4 of the discharge devices 61, 62 and 63 respectively.

The secondary winding 89 of transformer 86 is provided to develop a biasing voltage for discharge device 61. A rectifier 96 and a capacitor 97 are connected to secondary winding 89 and form a half wave rectifying circuit charging capacitor 97 to the polarity indicated in Figure 2. The positive terminal of capacitor 97 is connected through a cathode resistor 98 to cathode 75 of discharge device 61 while the negative terminal of this capacitor is connected through resistors 99 and 1011 respectively to control electrodes 73 and 72 of discharge device 61. The function of such a connection is to bias discharge device 61 substantially to cut-olf. The resistor 93 provides additional self bias. It will be remembered that discharge device 61 may be a gated beam type tube and if this type tube is used, it is possible to eliminate the above described biasing source including the half wave rectifying network and utilize a resistor such as resistor 98 exclusively to bias the device to cutoff.

Apparatus 66 includes a further transformer 161 having a primary winding 102 and a capacitor 103 connected to power input terminals 167 and 163. This transformer is a voltage regulating transformer and functions on the principle of saturating the core of the transformer to provide regulation. Capacitor 103 produces a resonant effect with primary 102 and increases the current flowing in the primary winding to thereby saturate the core of the transformer in a well known manner.

Transformer 191 includes a first secondary winding 104 and a second secondary winding 105. Winding 164 in conjunction with a rectifier 106 and a capacitor 107 forms a half wave rectifying circuit which charges capacitor 167 to the polarity indicated. The negative terminal of capacitor 107 is connected through resistor 93 to the cathode 75 of discharge device 61 while its positive terminal is connected through a plate load resistor 103 to the anode 71 of discharge device 61. Thus, the voltage across capacitor 107 supplies voltage for the anode-cathode circuit of discharge device 61 and also for devices 65 and 66.

The secondary winding 165 of transformer 164 is connected to terminals 164 and 165 and then to terminals 116 and 1110f unit 64. Unit 64 includes the discharge device 65, which may be a Thyratron, having anode 112, control electrode 113, a further electrode 114, cathode 115, and cathode heater 116. The unit 64 likewise includes the condition sensor 66. The electrode 63 of condition sensor 66 is connected to terminal 117 and from there to terminal 166 and to the positive terminal of capacitor 167. The second electrode 67 of condition sensor 66 is connected to the control electrode 113 of discharge device 65.

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It is a characteristic of a condition sensor 66 such as a Geiger tube that it has a high output impedance. In the apparatus of Figure 2 it is desired to locate the condition sensor 66 remote from the apparatus 60. In order to avoid the extension of leads to a remotely located Geiger tube having a high output impedance, the unit 64 is provided having a relatively low output impedance such that the unit 64 can conveniently be located at a substantial distance from the unit 60.

Discharge device 65 functions similar to discharge device 15 of Figure 1 in that it causes a voltage to be developed across resistors and 99 and resistors 120 and 121 whenever the Thyratron 65 fires. This applies a control voltage to discharge device 61 and also provides a voltage drop causing both Thyratron 65 and Geiger tube 66 to be extinguished.

The unit 64 includes a rectifier 122 and a capacitor 123 which in combination with secondary of transformer 101 form a half wave rectifying circuit to charge capacitor 124 to the polarity indicated. The positive terminal of this capacitor is connected directly to the cathode while the negative terminal thereof is connected through a resistor 123 to the control electrode 113 of discharge device 65. This voltage normally biases discharge device 65 to cutoff.

Operation of the apparatus of Figure 2 will now be described. Assuming first that the condition sensing device 66 is subjected to a random or background count, a pulse of current flows between electrodes 67 and 68. This current flow circuit can be traced from the upper terminal of capacitor 167 through terminal 166, terminal 117, conductor 140, condition sensor 66, conductor 141, resistor 123, rectifier 122, terminal 111, terminal 165, secondary winding 105, conductor 142, resistors and 100 in parallel with resistors 121 and 99, conductor 143, rectifier 96, and transformer secondary winding 89 to the lower terminal of capacitor 167. This current flow circuit causes a voltage to be developed across resistor 123 and to render discharge device 65 conductive. The current flow circuit for discharge device 65 can be traced from the upper terminal of capacitor 107 through terminals 166 and 117, anode 112 and cathode 115 of discharge device 65, terminals 110 and 164-, conductor 142, resistors 120 and 100 in parallel with resistors 121 and 99, conductor 143, rectifier 96, and transformer secondary winding 89 to the lower terminal of capacitor 107.

This latter current flow circuit causes a voltage to be developed across the resistors 166, 99, 120 and 121. The polarity of this voltage is such as to place a positive voltage on the upper terminal of each of the resistors 99 and 100. A positive voltage is immediately applied to control electrode 72. However, a capacitor is provided connected between the control electrode 73 and the cathode 75 of discharge device 61 and this capacitor in combination with resistor 121 functions as an integrating or time delay circuit to delay the application of the above mentioned voltage to the control electrode 73.

In the case such as assumed where the condition sensing device 66 is subjected to a random ionizing event, the control electrodes 72 and 73 do not have a positive voltage applied to them at the same time and discharge device 61 is not rendered conductive.

A capacitor 151 functions similar to capacitor 33 of Figure l in that it determines the firing rate of the Thyratron 65. In other words, when Thyratron 65 conducts through the above traced circuit, which includes capacitor 151 connected effectively in parallel with the resistor network 99, 166, 1213, and 121, substantially all of the voltage of the source constituted by capacitor 107 is dropped across this resistor network. Therefore capacitor 151 charges to substantially this full voltage. The function of capacitor 151 is to provide a certain decay time during which the charge on this capacitor is dissipated. This decay time determines the firing rate of Thyratron 65. Until this charge has been dissipated to a 9 certain value, an operating voltage is not available for either the Geiger tube 66 or the discharge device 65. While capacitor 151 remains charged, substantially all of the voltage available from capacitor 107 appears across capacitor 151 and a relatively low voltage is applied to devices 65 and 66. However, as soon as capacitor 151 discharges a sufiicient amount, an operative voltage is again applied to the anode of discharge device 65 and to the electrodes-f Geiger tube 66.

Assume now that Geiger tube 66 is subjected to an established flame, the gas within the Geiger tube ionizes 'anda pulse of current flows between the electrodes of the Geigeritube through the above traced circuit. This causes discharge device 65 to become conductive and a voltage is developed across resistors 99, 100, 120 and 121. In'th'is case however the Geiger tube 66 and the discharge device 65 will be conductive at periodic intervals and after atime delay a suiiiciently high voltage appears on capacitor 150,. thereby placing a voltage on control electrode 73 at the same time that a voltage is applied'to control electrode 72. This causes discharge device 61 to become conductive. The current flow circuit fo'rdischarge device 61 can be traced from the upper terminal ofcapacitor 107 through plate load resistor 108, an'ode 71 and cathode 75 of discharge device 61, cathode resistor 98, and conductor 152 to the lower terminal of capacitor 107. Y

This current flow circuit establishes a voltage across resistor 108 which is applied through filtering means 153 to control electrode 78 and cathode 79 of discharge device 62. The polarity of this voltage is such as to bias discharge device 62 to cut-off.

With dischargedevice 62 biased to cut-olf, a voltage no longer exists across resistor 90 and discharge device 63 becomes conductive. Conduction of discharge device 63 energizes winding 92 of relay 93 and movable switch blade 94 moves into engagement with stationary contact 95 to effect the required control function.

I The apparatus of Figure 2 has been constructed using components of the following values. It is intended that such values be exemplary only and they do not constitute a limitation of the present invention.

Discharge device 61 6BN6 Discharge device 62 /2 12AU7 Discharge device 63 /2 12AU7 Dischargedevice 65 5696 Secondary winding 85 v.A.C 450 Secondary winding 88 v.A.C 6.3 Secondary winding 89 v.A.C 12.6 Secondary winding 104 .v.A.C 22S Secondarywinding 105 v.A.C 6.3 Capacitor 107 mfd 4 Capacitor 97 mfd 4 Capacitor 150 mfd 4 Capacitor 151 mfd 0.05 Capacitor 124 mfd 4 Capacitor 180 mfd 0.25 Resistor 99 ohms 1M Resistor 100 do 1M Resistor 120 do 1M Resistor 121 do 1M Resistor 123 do M Resistor 98 do 3K Resistor 108 do 570K Resistor 181 do 22M Resistor 182 do 4.7M Resistor 90 do 10K Resistor 183 do 50K Resistor 184 do 57K From the above description, it can be seen that an improved condition sensing apparatus has been provided wherein a gated beam electron discharge device is utilized ina novel apparatus to discriminate against the background count of a condition sensor such as a Geiger tube. It will be recognized that the function of the gated beam electron discharge device, that is device 16 of Figure 1 and device 61 of Figure 2, can be likened to a pair of signal channels one of Which is delayed and both of which perform a control function only upon the coincidence of output voltage from the two signal channels.

Figure 3 is a schematic representation of a further modification of the present invention wherein the gated beam electron discharge device is replaced by a multielement device, for example, a tetrode 300 not having the gated beam characteristic.

In Figure 3, the Geiger tube 10 and the gas discharge device 15 in the quenching circuit for the Geiger tube are identical elements to the like numbered elements of Figures 1 and 2. The output of the quenching circuit is applied to the tetrode 300 having an anode 301, control electrodes 302 and 303 and cathode 304.

The output of the apparatus of Figure 3 consists of relay 305 having a winding 306 which is shunted by a capacitor 307. Relay 305 controls a switch identified by the reference numeral 308. The switch 308 may take a variety of forms and may produce a variety of control functions. However, for simplicity this has been labeled simply as output.

Operating voltage for the apparatus of Figure 3 is derived from a transformer 309 having a primary winding 310 and secondary windings 311 and 312., The primary winding 310 is adapted to be connected to a source of alternating voltage, not shown. The secondary winding 312 provides low voltage for energization of the filaments of the discharge devices 15 and 300. Furthermore, the winding 312 provides a biasing voltage for the discharge device 15. This can be seen by tracing a circuit from the lower terminal of secondary 312 through conductors 313 and 314, capacitor 315, rectifier 316 and conductor 317 to the upper terminal of secondary winding 312. From this above traced circuit it can be seen that capacitor 315 is charged to the polarity indicated in Figure 3 and discharge device 15 is biased substantially to cutofl, the positive plate of capacitor 315 being connected to the cathode 21 of discharge device 15 and the negative plate of this capacitor being connected through a resistor 318 to the control electrode 19 of discharge device 15.

Secondary winding 311 provides a source of high direct current operating voltage, in conjunction with rectifier 319 and capacitor 320. Capacitor 320 is charged to the polarity indicated on Figure 3.

Furthermore, secondary winding 311 is provided with a tap 321 and this portion of the secondary winding in conjunction with rectifier 322 and capacitor 323 provides' a source of biasing voltage for the control electrodes of discharge devices 300. Capacitor 323 is charged to the polarity indicated on Figure 3 and the positive plate of this capacitor is connected to the cathode 304 of discharge device 300. The negative plate of this capacitor is connected through resistor 324 to the control electrode 302 and through resistor 325 to the control electrode 303, thereby biasing discharge device 300 substantially to cut-off.

Upon capacitor 320 becoming charged, this charge is distributed to a further capacitor 326, this capacitor being charged to the polarity shown. The charging circuit for capacitor 326 can be traced from the upper plate of capacitor 320 through conductor 327, and capacitor 326 to conductor 328. At this point the charging circuit divides into two branches. The first of these branches consists of resistor 329 connected in series with the parallel connected resistor 324 and capacitor 330. The second branch of this circuit consists of resistor 331 connected in series with the parallel connected resistor 325 and capacitor 332. The circuit is then completed through conductor 333 to the lower plate of capacitor 11 320. From this above traced circuit it can be seen that the charging rate for capacitor 326 is determined by the impedance of the network including resistors 329, 331, 325 and 324. As will be apparent later, the charging rate of capacitor 326 determines the cycling or counting rate of Geiger tube 10.

The apparatus of Figure 3 is shown in its standby condition wherein operating voltage is applied to Geiger tube 10. The absence of an ionizing condition at the Geiger tube is indicated by relay 305 remaining in its deenergized condition. If it is assumed at this point that a random background count causes the Geiger tube 10 to become ionized, the capacitor 326 tends to discharge through the Geiger tube 10. This circuit can be traced from the upper plate of capacitor 326 through conductor 334, Geiger tube 10, conductor 335, resistor 318, rectifier 316, conductor 336, the filament of discharge device 15, and conductor 337 to the lower plate of capacitor 326. Since Geiger tube 10 conducts a relatively small magnitude current, the capacitor 326 is discharged but very little. The current flowing in this circuit however, develops a voltage across resistor 318 such that the cutoff bias on capacitor 315 is overcome and the discharge device is rendered conductive.

Upon this discharge device becoming conductive, the capacitor 326 is substantially short circuited through a circuit which can be traced from the upper plate of capacitor 326 through conductors 334 and 338, discharge device 15, and conductors 314 and 337 to the lower plate of capacitor 326. The capacitor 326 is therefore substantially completely discharged and therefore the voltage present across the anode and cathode of the Geiger tube 10 and across the anode and cathode of discharge device 15 drops substantially to zero, thereby quenching the Geiger tube 10 and extinguishing the discharge device 50.

The capacitor 326 now recharges through a circuit identical to that above traced, including the resistors 329, 331, 325 and 324. It will be noted that in this above traced circuit the resistors 324 and 325 are shunted by the capacitors 339 and 332. The capacitors 330 and 332 thereby function as an integrating or delay means to integrate or delay the voltage applied to the control electrodes 302 and 303. The resistors and capacitors making up this network are so selected that the voltage applied to one of the electrodes is integrated or delayed more than the voltage applied to the other. In this manner, the control voltages applied to the control electrodes 302 and 303 are integrated or delayed with respect to each other. The discharge device 300 therefore does not become conductive unless there is a coincidence of signals on the two control electrodes. This will occur only in the case of a sustained counting rate by the Geiger tube It) and will not occur in the case of a random background count of the Geiger tube. For example, a random background count of the Geiger tube may be effective to cause the control electrode 362 to have an operating voltage applied thereto due to the fact that this signal is not integrated to a very great extent. However, the integration accomplished by capacitor 332 would in this case be relatively large and no voltage would be applied to the control electrode 303 at this time, thereby maintaining the discharge device 390 cutoff.

If it is now assumed that sustained counting is experienced by the Geiger tube It), such as caused by a flame or other ionizing condition present at the Geiger tube, the above explained cycle of events occurs at a relatively rapid rate, determined by the recharging time of the capacitor 326 since it is remembered that the Geiger tube 15 is not again effective to experience an ionizing event until the capacitor 326 has been charged to apply an operating voltage to the Geiger tube. This recharging current for the capacitor 326 develops a voltage across the resistors 325 and 324, at a rate determined by the capacitors 332 and 330, which is efiective to overcome the biasing voltage present on capacitor 323. In the event of a sustained count of the Geiger tube 10, the discharge device 360 is rendered conductive to energize the relay 305.

The apparatus of Figure 3 has been constructed using components of the following values. It is intended that such are exemplary only and they do not constitute a limitation of the present invention.

Discharge device 15 5696 Discharge device 300 6AS5 Secondary winding 311 volts 285 Secondary winding 312 do 6.3 Capacitor 315 mfd 4 Capacitor 326 mfd .05 Capacitor 332 mfd 4 Capacitor 330 mfd 4 Capacitor 307 mfd Capacitor 320 mfd 4 Resistor 318 megohrns 10 Resistor 329 do .47 Resistor 331 do .82 Resistor 325 do .82 Resistor 324 do 10 From the above description it can be seen that Figure 3 provides an improved condition sensing apparatus wherein the gated beam tube utilized in Figures 1 and 2 is replaced by more conventional type tetrode not having the gated beam characteristics and in which the apparatus discriminates against the background count of a condition sensor such as the Geiger tube by providing an integrated signal to both of the control electrodes of this tetrode, one of the signals being integrated more than or relative to the other.

These and other modifications of the present invention will be apparent to those skilled in the art and it is intended that the present invention be limited solely by the scope of the appended claims.

I claim as my invention:

1. A condition detector comprising: a Geiger tube type condition sensor, a source of voltage, impedance means; means connecting said condition sensor, said source of voltage and said impedance means in a series circuit to thereby cause a voltage to appear across said impedance means when said condition sensor is subjected to a condition which causes said condition sensor to ionize; first circuit means connected to said impedance means; second circuit means including integrating means connected to said impedance means; and voltage responsive means connected to said first and second circuit means and arranged to respond only to a coincidence of voltage from said first and second circuit means.

2. In combination; a source of voltage, impedance means, a condition sensor having a pair of spaced electrodes in an ionizable gaseous medium; means connecting said source of voltage, said impedance means and said condition sensor in a series circuit to thereby develop a pulse of voltage across said impedance means each time said condition sensor is subjected to a condition which causes ionization of the gaseous medium; an integrating circuit having an input and an output, means connecting said integrating circuit input to said impedance means; and comparing means connected to said integrating circuit output and said impedance means to comparing the voltages thereof, said comparing means responding only to a coincidence of voltage at said impedance means and at said integrating circuit output to thereby discriminate against an occasional rate of ionization of the gaseous medium of said condition sensor.

3. In combination; a source of voltage, impedance means, a condition sensor having a pair of spaced electrodes in an ionizable gaseous medium; means connecting said source of voltage, said impedance means and said 13 condition sensor in a series circuit to thereby develop a pulse of voltage'across said impedance means each time said condition sensor is subjected to a condition which causes ionization of the gaseous medium; an electron discharge device having a pair of control electrodes, biasing means, means connecting said biasing means to each of said first and second control electrodes to thereby bias said electron discharge device substantially to cutoff; time delay means, circuit means connecting said first control electrode through said time delay means to said impedance means, circuit means having no time delay connecting said second control electrode to said impedance means, the manner of said last named circuit means being such as to render said electron discharge device substantially conductive upon a coincidence of voltage appearing on said first and second electrodes.

4. Condition sensing apparatus comprising; electrically operable condition responsive means, electrical means connected to said condition responsive means and having an output with a voltage thereon indicative of the condition to which the condition responsive means is subjected, a sharp cutoff electron discharge device having a pair of control electrodes, biasing means connected to said electron discharge device and biasing said discharge device substantially to cutoff, first circuit means having substantially no time delay connecting the first control electrode of said discharge device to said output, and second circuit means having a time delay connecting the second control electrode of said discharge device to said output to thereby render said discharge device conductive only upon a coincidence of signals appearing at said first and second control electrodes.

5. Condition sensing apparatus comprising; a source of direct current voltage having a positive and a negative terminal, first resistance means, a Geiger tube having an anode and a cathode; circuit means connecting said Geiger tube, said first resistance means and said source of direct current voltage in a series circuit; capacitance means, means connecting said capacitance means in parallel with'said first resistance means; a first electron discharge device having an anode, a cathode and a control electrode; biasing means connected to said first discharge device to'render it substantially nonconductive; means connecting said discharge device cathode to the negative terminal of said direct current source of voltage, means connecting said discharge device control electrode to the cathode of said Geiger tube, means connecting said discharge device anode to the anode of said Geiger tube; said Geiger tube when subjected to a condition causing ionization thereof thereby rendering said first electron discharge device conductive, said first discharge device when conductive causing a voltage drop to exist across said first resistance means to thereby extinguish said Geiger tube, the time within which an operating voltage is again supplied to said Geiger tube being determined by the time constant of said first resistance means and said capacitance means; a gated beam electron discharge device having a pair of control electrodes and an anode and cathode; biasing means connected to said gated beam discharge device to render it substantially nonconductive; second resistance means, means connecting a first control electrode of said gated beam discharge device through said second resistance means to said first resistance means, third resistance means, means connecting a second control electrode of said gated beam discharge device through said third resistance means to said first resistance means, further capacitance means, means connecting said furthere capacitance means from said second control electrode to said cathode of said gated beam discharge device, means connecting the cathode of said gated beam discharge device to said first resistance means; and means controlled by the anode to cathode current of said gated beam discharge device, which current flows only when a coincidence of signals appears at the first and second control electrodes of said gated beam discharge device.

6. Condition sensing apparatus comprising; a Geiger tube, circuit means connected to be controlled by said Geiger tube and arranged to derive an individual output signal pulse at the output thereof for each period of ionization of said Geiger tube, a first signal channel, means connecting said first signal channel to the output of said circuit means to provide a first signal, a second signal channel including time delay means, means connecting said second signal channel to the output of said circuit means to produce a second signal which is delayed relative to said first signal, and signal responsive means connected to said first and second signal channels and controlled jointly by said first and second signals, said signal responsive means performing a control function only upon a predetermined time relation existing between said first and second signals.

7. A condition detector comprising; a Geiger tube type condition sensor, a source of voltage, impedance means, circuit means connecting said condition sensor, said source of voltage and said impedance means in a circuit to thereby cause a voltage to appear across said impedance means when said condition sensor is subjected to a condition which causes said condition sensor to ionize; first circuit means connected to said impedance means; second circuit means including integrating means connected to said impedance means; and voltage responsive means connected to said first and second circuit means and arranged to respond only upon a predetermined time relation existing between the voltage from said first and second circuit means.

8. Condition sensing apparatus comprising; a Geiger tube, circuit means connected to be controlled by said Geiger tube and arranged to derive an individual output signal pulse at the output thereof for each period of ionization of said Geiger tube, a first signal channel including first integrating means, means connecting said first signal channel to the output of said circuit means to provide a first signal, a second signal channel including second integrating means, means connecting said second signal channel to the output of said circuit means to provide a second signal, said first and second integrating means providing different degrees of integration, and signal responsive means connected to said first and second signal channels and jointly controlled by said first and second signals, said signal responsive means performing a control function only upon a predetermined time relation existing between said first and second signals.

9. Condition sensing apparatus comprising; a Geiger tube, circuit means connected to be controlled by said Geiger tube and arranged to derive an individual output signal pulse at the output thereof for each period of ionizationof said Geiger tube, a first signal channel including first delay means, means connecting said first signal channel to the output of said circuit means to provide a first signal, a second signal channel including second delay means, means connecting said second signal l channel to the output of said circuit means to provide a second signal, and signal responsive means connected to said first and second signal channels and jointly controlled by said first and second signals, said signal responsive means performing a control function only upon a predetermined time relation existing between said first and second signals.

10. A condition detector comprising; a Geiger tube type condition sensor, quenching circuit means for said Geiger tube having an individual output signal pulse at the output thereof for each period of energization of said Geiger tube, an electron discharge device having a first and second control electrode, means biasing said electron discharge device substantially to cut-off, first circuit means including a first integrating network connecting said first control electrode to the output of said quenching circuit, further circuit means including a second integrating network connecting said second control electrode to the output of said quenching circuit, said first and second integrating networks providing ditferent time periods of integration to thereby delay the voltage applied to one of the control electrode-s with respect to the voltage applied to the other of the control electrodes, and voltage responsive means connected to the output of said electron discharge device and arranged to respond only to a predetermined time relation existing between the voltage from said first and second integrating means.

UNITED STATES PATENTS Rabinow Mar. 17, 1953 Exner Oct. 18, 1955 Joyce et a1. Sept. 4, 1956 Carbaugh May 6, 1958 Orthuber et al. Oct. 14, 1958 

